1. Field of the Invention
The present invention relates to a longitudinally pumped laser including a pumping module with a pumped light source and an input optic, and a resonator with an input mirror, a laser medium and an output mirror. The term "longitudinally pumped laser" denotes that the pumped light produced by the pumped light source is coupled to the resonator in an orientation parallel or at least approximately parallel to the direction of the laser beam produced by the laser. The light may be coupled, for example, by the input mirror of the resonator.
2. Description of Related Art
U.S. Reissue Pat. No. Re. 34,729 discloses (as shown in FIG. 2a thereof) a laser of the type wherein the pumped light source, input optic and resonator are disposed on a common optical axis. In such a laser all components are usually adjusted so that the path of the pumped light ray between the pumped laser and the mode volume of the pumped laser is optimally adapted so that the pumped light from the laser is absorbed in this mode volume as completely as possible.
A drawback of this arrangement is that pumped light can be retroreflected to the pumped light source by the surface of the resonator facing the pumping module. Furthermore, a portion of the light produced by the laser can exit the resonator as leakage radiation through the first reflecting surface and likewise impinge on the pumped light source. This retroreflected pumped light and/or leakage radiation of the laser can impair the functioning of the pumped light source. The impinging radiation causes heating of the pumped light source, which can influence the intensity and wavelength of the pumped light and damage or even destroy the pumped light source.
If the pumped light source is a laser, specifically a laser diode, and the retroreflected pumped light hits the active surface of the pumped light source (pumping laser), an additional resonator can form between the exit surface of the pumping laser and the entrance surface of the pumped laser. This additional resonator will be unstable and disturb the modes of the pumping laser, causing its power and wavelength to fluctuate and thus resulting in impaired functioning of the pumped laser.
If the pumped laser operates in pulsed mode, the leakage radiation can reach very great intensity even at a very small leakage rate of the resonator and lead to damage or destruction of the pumped light source.
U.S. Pat. No. 5,315,613 discloses a diode-pumped solid-state laser wherein the optical axis of the laser diode serving as a pumped light source is shifted parallel to the optical axis of the input optic. This is intended to reduce the light retroreflected to the laser diode. A drawback of this arrangement is that the acentric transmission of the input optic leads to image defects which can have an adverse effect on the coupling of the pumped ray into the mode volume. Pumped light sources (specifically laser diodes) are generally produced as a single unit with a corresponding input optic adjusted centrically to the pumped light ray. Acentrically adjusted input optics require elaborate special production of the pumping module, which increases costs.
European Patent No. 632 551 A1 discloses a solid-state laser having a resonator constructed from an output mirror and an end mirror disposed therebeside as well as a crystal serving as a laser medium disposed opposite these two mirrors. The side of the crystal facing away from the mirrors is metalized and the crystal is mounted with this metalized face on a cooling surface. If the laser is to be pumped approximately longitudinally, the pumped light must be irradiated into the surface of the crystal facing the two mirrors. Since the pumped light source can only be disposed at the side of the two mirrors, irradiation is possible only at a certain angle to the optical axis of the resonator (see FIG. 21 of EP 632 551 A1). In this known laser, irradiation of the pumped light at an angle to the optical axis of the resonator thus necessarily results from the arrangement of the other components and is not used for the purpose of keeping reflected pumped light away from the pumped light source. Quite the contrary, the mirror (element 202) shown in FIG. 21 of EP 632 551 A1 causes the pumped light reflected from the surface of the crystal to be retroreflected into the pumped light source.